From: Vincent MAILHOL <mailhol.vincent@wanadoo.fr>
To: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>,
netdev <netdev@vger.kernel.org>,
David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
linux-can <linux-can@vger.kernel.org>,
kernel@pengutronix.de
Subject: Re: [net-next 09/17] can: length: can_fd_len2dlc(): simplify length calculcation
Date: Thu, 14 Jan 2021 18:16:14 +0900 [thread overview]
Message-ID: <CAMZ6RqLKYnGDePueN1ftL9a47Qf-ZR7bc4eLGwzCkncsD6ok2Q@mail.gmail.com> (raw)
In-Reply-To: <2f3fff1a-9a50-030b-6a29-2009c8b65b68@hartkopp.net>
On Tue. 14 Jan 2021 at 17:23, Oliver Hartkopp <socketcan@hartkopp.net> wrote:
> On 14.01.21 02:59, Vincent MAILHOL wrote:
> > On Tue. 14 Jan 2021 at 06:14, Marc Kleine-Budde <mkl@pengutronix.de> wrote:
> >>
> >> If the length paramter in len2dlc() exceeds the size of the len2dlc array, we
> >> return 0xF. This is equal to the last 16 members of the array.
> >>
> >> This patch removes these members from the array, uses ARRAY_SIZE() for the
> >> length check, and returns CANFD_MAX_DLC (which is 0xf).
> >>
> >> Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> >> Link: https://lore.kernel.org/r/20210111141930.693847-9-mkl@pengutronix.de
> >> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
> >> ---
> >> drivers/net/can/dev/length.c | 6 ++----
> >> 1 file changed, 2 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
> >> index 5e7d481717ea..d695a3bee1ed 100644
> >> --- a/drivers/net/can/dev/length.c
> >> +++ b/drivers/net/can/dev/length.c
> >> @@ -27,15 +27,13 @@ static const u8 len2dlc[] = {
> >> 13, 13, 13, 13, 13, 13, 13, 13, /* 25 - 32 */
> >> 14, 14, 14, 14, 14, 14, 14, 14, /* 33 - 40 */
> >> 14, 14, 14, 14, 14, 14, 14, 14, /* 41 - 48 */
> >> - 15, 15, 15, 15, 15, 15, 15, 15, /* 49 - 56 */
> >> - 15, 15, 15, 15, 15, 15, 15, 15 /* 57 - 64 */
> >> };
> >>
> >> /* map the sanitized data length to an appropriate data length code */
> >> u8 can_fd_len2dlc(u8 len)
> >> {
> >> - if (unlikely(len > 64))
> >> - return 0xF;
> >> + if (len > ARRAY_SIZE(len2dlc))
> >
> > Sorry but I missed an of-by-one issue when I did my first
> > review. Don't know why but it popped to my eyes this morning when
> > casually reading the emails.
>
> Oh, yes.
>
> The fist line is 0 .. 8 which has 9 bytes.
>
> I also looked on it (from the back), and wondered if it was correct. But
> didn't see it either at first sight.
>
> >
> > ARRAY_SIZE(len2dlc) is 49. If len is between 0 and 48, use the
> > array, if len is greater *or equal* return CANFD_MAX_DLC.
>
> All these changes and discussions make it very obviously more tricky to
> understand that code.
>
> I don't really like this kind of improvement ...
>
> Before that it was pretty clear that we only catch an out of bounds
> value and usually grab the value from the table.
I understand your point: all three of us initially missed that
bug. But now that it is fixed, I would still prefer to keep
Marc's patch.
Yours sincerely,
Vincent
> >
> > In short, replace > by >=:
> > + if (len >= ARRAY_SIZE(len2dlc))
> >
> >> + return CANFD_MAX_DLC;
> >>
> >> return len2dlc[len];
> >> }
next prev parent reply other threads:[~2021-01-14 9:17 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-13 21:13 pull-request: can-next 2021-01-13 Marc Kleine-Budde
2021-01-13 21:13 ` [net-next 01/17] MAINTAINERS: adjust entry to tcan4x5x file split Marc Kleine-Budde
2021-01-13 21:13 ` [net-next 02/17] MAINTAINERS: CAN network layer: add missing header file can-ml.h Marc Kleine-Budde
2021-01-13 21:13 ` [net-next 03/17] can: dev: move driver related infrastructure into separate subdir Marc Kleine-Budde
2021-01-13 21:13 ` [net-next 04/17] can: dev: move bittiming related code into seperate file Marc Kleine-Budde
2021-01-13 21:13 ` [net-next 05/17] can: dev: move length " Marc Kleine-Budde
2021-01-13 21:13 ` [net-next 06/17] can: dev: move skb related " Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 07/17] can: dev: move netlink related code " Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 08/17] can: length: convert to kernel coding style Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 09/17] can: length: can_fd_len2dlc(): simplify length calculcation Marc Kleine-Budde
2021-01-14 1:59 ` Vincent MAILHOL
2021-01-14 7:34 ` Marc Kleine-Budde
2021-01-14 8:23 ` Oliver Hartkopp
2021-01-14 9:16 ` Vincent MAILHOL [this message]
2021-01-14 17:03 ` Oliver Hartkopp
2021-01-15 1:57 ` Vincent MAILHOL
2021-01-13 21:14 ` [net-next 10/17] can: length: canfd_sanitize_len(): add function to sanitize CAN-FD data length Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 11/17] can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 12/17] can: dev: extend struct can_skb_priv to hold CAN frame length Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 13/17] can: dev: can_put_echo_skb(): extend to handle frame_len Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 14/17] can: dev: can_get_echo_skb(): extend to return can frame length Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 15/17] can: dev: can_rx_offload_get_echo_skb(): " Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 16/17] can: dev: can_put_echo_skb(): add software tx timestamps Marc Kleine-Budde
2021-01-13 21:14 ` [net-next 17/17] can: tcan4x5x: remove __packed attribute from struct tcan4x5x_map_buf Marc Kleine-Budde
2021-01-14 7:32 ` pull-request: can-next 2021-01-13 Marc Kleine-Budde
2021-01-14 7:56 pull-request: can-next 2021-01-14 Marc Kleine-Budde
2021-01-14 7:56 ` [net-next 09/17] can: length: can_fd_len2dlc(): simplify length calculcation Marc Kleine-Budde
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